POA and guardianship are VERY DIFFERENT things.
If a person grants power of attorney to another person, both can make decisions, transactions, etc. Thus, if an individual wants not to live in a nursing home, a person with power of attorney cannot make it happen. If the individual who granted POA is not incapacitated, that person may revoke the POA. If that individual is incapacitated, a court may revoke the POA.
If an individual is another's guardian, it means that a court has determined that the ward is incapacitated and that the guardian was appointed by the court. Usually, the court retains authority to monitor the situation (audit the assets and expenditures and income of the estate, review the physical and mental well-being of the ward, etc.).
If you believe an adult is being exploited, go to your state's agency on adult protective services. Or consult your attorney to see if you can apply to be that person's guardian.
years of experience in probate court